We have previously described a range of improved techniques for increasing reliability and efficiency in photovoltaic inverters (see, for example, WO2007/080429 and others of our published patent applications).
We now particularly address problems which can arise with so-called microinverters. A microinverter is an inverter dedicated to one or a few PV panels, and may be defined as an inverter having a power rating suitable for connection to less than 10 or less than 5 panels (for example less than 1000 watts, often less than 600 watts) and/or as an inverter having a dc input voltage which is less than half a peak-to-peak voltage of the ac mains, more typically less than 100 volts dc or less than 60 volts dc. One of the advantages of a microinverter is that it can be physically located close to the PV panel or panels to which it is connected, thus reducing the voltage drop across the connecting cables (which can be significant). However, locating a microinverter adjacent to or on a PV panel brings other difficulties, in particular because such locations are subject to extreme temperature and environmental conditions including, for example, water, ice, humidity, and dry heat (depending upon the installation, up to or above 80° C.).
The very large temperature excursions, and in particular the extremes of high temperature which may be encountered, create particular difficulties. In addition a microinverter generates heat which increases the internal temperature of the electronic components above the local ambient conditions. Simple potting of the electronic components can in principle help to address some of these issues but in practice air bubbles and the like can give rise to local temperature hotspots (caused by the low thermal conductivity of air), which can lead to reliability problems and premature failure of the inverter.
There therefore exists a need for improved manufacturing techniques for solar photovoltaic inverters, in particular microinverters.